An employee or a staff member who doesn't seem to understand no matter how much we explain it.

Instead of feeling annoyed at them or feeling discouraged, we have to remember that other people are doing their best as well:

A customer who doesn't buy from us is probably weighing her options to make sure she is buying the best product out there. Why not prepare a comparison for her beforehand?

A prospect who doesn't answer our phone calls is probably not comfortable taking calls from a stranger. Why not introduce yourself to him, tell him how you got his details, and tell him what he should expect from a conversation with you?

A client who sets an unreasonable budget may have been pressured by her boss to keep costs within their internal budget. Maybe she is looking to get the best deal given a limited budget. Instead of forcing your fees on her, why not find a way to work around the budget with her? Assure her that you are on her side. Maybe you can opt not to include some of your services in a package (assuming that, overall, the package still provides a great experience) to keep within the budget or respectfully walk away from the deal altogether.

A boss who doesn't seem to listen may have other things in mind. Why not do a good job as he specified, deliver more than he is asking for, and talk to him about it some other time? You may also want to do your work like how his own boss wants it. Chances are he also has a boss he needs to report to and give his best output to.

An employee or a staff member who doesn't seem to understand may be going through a tough time. Maybe she is just trying her best to cope with her personal problems by being at work. Why not ask her how she is doing and tell her that, hopefully, it will not affect her output? It may also help to assure her that you are on her side as well.